JPS6290820A - Cathode for electron tube - Google Patents

Abstract

PURPOSE:To increase the life of a cathode for an electron tube by coating a base principally composed of nickel with an electron-emitting substance layer which is principally composed of the oxides of alkaline earth metals including barium and containing 0.1-20wt% of a complex oxide of the oxides of rare earth metals. CONSTITUTION:A suspension is prepared by adding 0.1-20wt% of a Ba2SC4O9 powder or Ba3Y4O9 powder to a ternary carbonic salt of barium, strontium and calcium. This suspension is applied to a base 1 principally composed of nickel by spraying in a thickness of about 80 microns. Next, the base 1 is coated with an electron-emitting substance layer 2 through the decomposition process from carbonate to an oxide and an activation process whereby the oxide is reduced partially. Thus, it is possible to increase the life of the cathode under the operation at high current density.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an electron tube cathode used in a di-braun tube for TV, and particularly relates to an improvement of an electron emissive material layer.

[Conventional technology]

Figure 2 shows a cathode used in a conventional di-cathode ray tube for TVs. A low cylindrical base made of nickel (
2) is an electron emitting material layer which is attached to the bottom upper surface of this substrate and is made of an alkaline earth metal oxide containing at least barium (HM) and also strontium (S') and/or calcium (Ca). , (3) is the above substrate (
A heater (3) disposed within 1) is used to emit thermoelectrons from the electron emitting material layer (2) by heating.

In the electron tube cathode configured in this way, the base film
Electron radiation to? The J layer (2) is deposited as follows. First, alkaline earth metals (Ba.

A suspension consisting of carbonates of Sr, Ca) is applied to the substrate (11) and heated by a heater (3) during the evacuation process.

At this time, the alkaline earth metal carbonate turns into an alkaline earth metal oxide. Thereafter, by reducing a part of the alkaline earth metal oxide and activating it to have semiconducting properties, an electron emitting material layer ( 2) is coated.

In this activation step, some of the alkaline earth metal oxides react as follows.

Reducing elements such as silicon and magnesium contained in the substrate (substrate +1) move to the interface between the alkaline earth metal oxide and the substrate (11) by diffusion, and react with the alkaline earth metal oxide. For example, if barium oxide (Bib) is used as the alkaline earth oxide, it reacts as shown in the following formulas (1) and (2).

BaO+ 1/2S i -Ba+1/2S iO*
---filBaO10Mg = Ba+Mg
O... --(21 As a result of this reaction, a part of the alkaline earth metal oxide deposited on the substrate (1) is reduced,
It becomes an oxygen-deficient semiconductor, with a single pole temperature of 700-800℃.
At an operating temperature of 0.5 to 0.8 A/cd, an electron emission of 0.5 to 0.8 A/cd is obtained. However, in the electron tube cathode formed in this way, the electron emission is 0.5 to 0.8 A/c.
A current density higher than lr cannot be obtained. The reasons for this are as follows. In other words, when a part of the alkaline earth metal oxide is subjected to a reduction reaction, the above +11
(As is clear from formula 21, 5ins at the interface between the substrate and the alkaline earth metal oxide layer, 0 or Bad for M,
A composite oxide H (intermediate l1l) of 5iO8 is formed, and this intermediate layer becomes a high-resistance layer and obstructs the flow of current. 2) It is considered that sufficient barium (Ba) is not generated because it prevents the barium (Ba) from diffusing toward the surface side.

In addition, as a conventional cathode for electron tubes, JP-A-2094
In Publication No. 1, the structure is similar to that shown in Figure 2, in which the thickness of the substrate (1) is made thinner in order to obtain rapid action of the cathode, and the temperature of the reducing agent during its life is reduced. It prevents moisture and the substrate (1
) In order to prevent a decrease in the strength of the substrate (11), lanthanum is dispersed in the form of LaNi5 and Lm,0.

[Problem that the invention seeks to solve]

In the electron tube cathode constructed in this way, during operation, electrons are generated near the interface between the substrate (1) and the electron emitting material fm f21, particularly between the nickel crystal grain boundary near the surface of the substrate (1) and the above interface by about 10 μm. Since the above-mentioned intermediate layer is segregated inside the emissive material layer (2), the flow of current and the diffusion of reducing elements toward the surface of the electron emissive material layer (2) are hindered, and sufficient There was a problem that electron emission characteristics could not be obtained.

In addition, in the case of the latter, since LaNi5 and Lm, 0° are included in the production of the substrate (rl) whose main component is nickel, LaNi5 and Lo in the substrate (1) are
, 0. Variations in the content of these substances were likely to occur.

This invention has been made in view of the above points, and is intended to prevent the intermediate layer made of a composite oxide from being concentrated near the interface between the substrate and the electron emitting material layer under high current density. The object of the present invention is to obtain a cathode for an electron tube that has stable emission characteristics over a long period of time and has high productivity and reliability.

[Means for solving problems]

The cathode for an electron tube according to the present invention has an alkaline earth metal containing at least barium as a main component, and has a content of 0.1 to 20%
An electron-emitting material layer containing a composite oxide of a rare earth metal oxide and an alkaline earth metal oxide in the amount by weight is formed on a substrate mainly composed of nickel.

[For production]

In this invention, 0 contained in the electron emitting material layer
, when the composite oxide of rare earth metal oxide and alkaline earth metal oxide in an amount of 1 to 201i is activated to form an electron emitting material layer on a substrate, the alkaline earth metal carbonate decomposes. This prevents the oxidation of the substrate when barium oxide undergoes a dissociation reaction during operation or as a cathode, and appropriately controls the diffusion of reducing elements contained in the substrate into the electron emitting material layer. In addition, the intermediate layer made of a composite oxide made of a reducing element is prevented from being formed intensively near the interface between the substrate and the electron emitting material layer, and the intermediate layer is dispersed within the electron emitting material layer. .

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. In the figure, (2) is deposited on the top surface of the bottom of the substrate (1), contains at least barium, and also contains strontium or/and calcium as a main component, and contains 0.1 It is an electron emitting material layer containing ~20% by weight of an alkaline earth/rare earth metal composite oxide ((2) such as barium scandate (BasSCaOs) = barium ytlate (BaxYaOe).

Next, in the cathode for an electron tube configured in this way, the method of depositing the electron emissive material layer (2) on the substrate (11) will be explained. ,0, powder or Ba1
YaO@ powder is added and mixed in a desired weight % (weight % assuming all of the above ternary carbonates become oxides) to create a suspension. This suspension was applied to a substrate containing nickel as a main component +11
The electron emitting material layer is applied by spraying to a thickness of about 80 microns, and then, as with conventional products, the carbonate is decomposed into oxides and activated to reduce some of the oxides. (2) is applied to the base (1).

The electron emitting material layer (2) deposited by such a method may contain Ha, 5C40, Ba, Y, 0. We created various cathodes for electron tubes with various contents of The results shown in Figures and Figure 4 were obtained. Figure 3 shows an electron emitting material layer containing 5% by weight of Ba3SC40s (
2) Electron tube cathode with 10% by weight Ba, Y2O
.

Life characteristics of a cathode for an electron tube having an electron emitting material layer (2) containing , and a conventional example having a cathode emitting material layer for an electron tube (2) containing no alkaline earth/rare earth metal composite oxide This shows the relationship between the life characteristics of

As is clear from FIG. 3, the device of this embodiment containing an alkaline earth/rare earth metal composite oxide exhibits less emission deterioration during high current density operation than the conventional device.

In addition, Fig. 4 shows that the current density is 2 when the current density is 0.86 A/cd (assumed to be 1) in an electron tube cathode having an electron emitting material R(2) with various addition ratios of Ba and 5C40°. A life test was conducted under the conditions of 60%, 3.1x, and 4x, and the current density and initial emission reduction were
The graph shows the relationship between the emission reduction ratio and the emission reduction ratio at 0 hours. As can be seen from this Figure 4, Ba3SCaOe
When the addition rate is 0.1% by weight or higher, it has the effect of preventing emission reduction under high current density operation, and although not shown in the figure, this effect is maintained up to an addition rate of 20wt% for Ba, 5C40, and It could be confirmed. However, if this addition rate exceeds 20% by weight, it becomes difficult to achieve a stable reduction in emissions unless immersion through the manufacturing process or aging for a long time is performed, which is impractical. Therefore, the content of the alkaline earth/rare earth metal composite oxide in the electron emitting material j1 (21) needs to be 0.1 to 20% by weight. The effect of raising energy was noticeable within the range.

In order to investigate in detail the effect of containing an alkaline earth/rare earth metal composite oxide in the electron emitting material layer (2), the experimental results shown in Figure 8 show that after measuring the emission current for 6000 hours, and 7% by weight Ba, 5C4
A cross section of an electron tube cathode having an electron emitting material layer (2) containing 0,
As a result of analysis by PM illusion, in the conventional electron tube cathode having an electron emitting material layer (2), the substrate (1) is located near the interface between the nickel base (1) and the electron emitting material layer (2). ) It was confirmed that the reducing agents Si and Mg contained in the oxide were segregated, and these metals are thought to exist as oxides or composite oxides. That is, in the conventional product under high current density operation, the substrate (11
and near the interface between the electron emitting material layer (2) and the grain boundaries in the substrate (1).

A layer of MgO and a composite oxide thereof is formed, and a bad layer is formed from the interface to the electron emitting material layer (2).

It can be seen that a composite oxide layer of MgO, 5ins, is formed. The above-mentioned Sin, .MgO layer and BaO.Si01 layer contain electron emitting material H from within the substrate (1).
(2) It suppresses the diffusion rate of Si and Mg, which are reducing agents, and is highly insulating, which obstructs the flow of current, eventually leading to wear and tear due to dielectric breakdown within the electron emitting material. It is something.

On the other hand, in the cathode for an electron tube having an electron emitting material layer (2) containing Ba3SCaO@, which is the present example, SI, which is a reducing agent, was contained in the base (1).

The ME is evenly distributed, and as in the conventional example, the electron emitting substance Ji! There are no peaks of these reducing agents near the interface with f(21). This is considered to be due to the following reason.

The reducing elements Si and Mg in the substrate (1) react with the electron-emitting substance fli (2) at the substrate interface, and Si and Mg are generated near the interface.
g, MgO or a composite oxide of these and BaO is formed, but when Ba and 5C40 are contained as in this example, 5i01. MgO etc. and Ba, 5C4
0, reacts and Si again.

The electron-emitting material layer (2) facilitates movement within the electron-emitting material layer (2). In other words, the alkaline earth/rare earth metal composite oxide in the electron emitting material layer (2) moderately controls the rate of diffusion of the reducing element into the electron emitting material, even after long-term operation under high current density. Stable and good emission characteristics can be maintained. Therefore, if less than 0.1% by weight of alkaline earth/rare earth metal composite oxide is added, the base (1)
near the interface of SiO,.

The effect of suppressing the formation of an oxide layer of MgO is insufficient, and the emission characteristics begin to deteriorate.

Moreover, when more than 20% by weight is added, the relative content in the electron emitting material layer increases, resulting in a decrease in emission characteristics.

In the above examples, Ba, 5C40, Ba, and Y are used as the upper alkali/rare earth metal composite oxides.

0, was explained, but Ba5C10,, Ba
Y20a.

5r3SCaO@, Ca5SC40,, Ba3Ce,
0. Similar effects can be obtained with other oxides such as.

As described above, according to the present invention, a cathode can be manufactured under almost the same manufacturing conditions as conventional ones, and the state of dispersion of the alkaline earth/rare earth metal composite oxide can be controlled relatively easily.

〔Effect of the invention〕

As described above, the present invention is characterized in that an electron emitting material layer mainly composed of an alkaline earth metal oxide containing at least barium is coated on a substrate and contains 0.1 to 20% by weight of upper alkali metals and rare earth metals. Since the metal composite oxide is contained, the electron emitting material layer can operate at a current density 2 to 4 times higher than the conventional one in which the upper alkaline metal/rare earth metal composite oxide is not included in the electron emitting material layer. This has the effect of providing a highly reliable cathode for an electron tube that has a long life, is inexpensive, and has few manufacturing restrictions.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing an embodiment of the present invention, Fig. 2 is a sectional view showing a conventional cathode for an electron tube, Fig. 3 is a diagram showing the relationship between life test time and emission current, and Fig. 4 is a sectional view showing an example of the present invention. FIG. 3 is a diagram showing the relationship between current density and emission current ratio. In the figure, fil is a base, and (2) is an electron emitting material layer. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] The main component is nickel, the main component is an alkaline earth metal oxide containing at least barium, and the main component is 0.1~
A cathode for an electron tube, characterized in that an electron emitting material layer containing 20% by weight of a composite oxide of a rare earth metal oxide and an alkaline earth metal oxide is deposited.